Dense Transducer Array

High-frequency wideband transducer system for underwater sonar applications

February 1, 2011

Naval Undersea Warfare Center, Newport, RI

A dense transducer array is an acoustic transducer with relatively high operational bandwidth. It includes a cable harness component that provides and organizes various conductors within piezocomposite substrates to form transducer arrays with minimum impact on electroacoustic performance. Several underwater sonar applications exist for high-frequency wideband transducer arrays having individual elements. In order to form and steer acoustic beams with an array of individual elements, the array elements must be spaced not more than one-half the acoustic wavelength at the highest frequency of interest. This implies, for square-shaped elements at least, that the elements' lateral dimensions are inversely proportional to frequency. Therefore, for fully populated radiating apertures, the number of elements increases exponentially as the spacing decreases.

As piezocomposite arrays move to higher operational bandwidths and frequencies, the element center-to-center spacing decreases as the number of elements forming the array aperture increases. The result is a need for a component that organizes the numerous electrical wires found in piezocomposite arrays.

A piezoceramic transducer preform can be created by machining away material between preform posts and leaving a base portion of the piezoceramic material on a bottom side of the block and preform posts on a top side of the block. A generalized top surface is defined by the tops of the preform posts opposite from the surface defined by the base. Conductors are inserted in the gaps between the preform posts with the ends of the conductors extending through apertures formed in the base, and beyond the general top surface of the preform posts. The combined base, preform post, and conductor volume is filled with a liquid polymer, which is allowed to harden. Any conductor or polymer extending above the general top surface is removed. The base and conductors extending beyond a selected transducer volume are removed leaving a bottom preform surface. Electrodes are provided on the top preform surface and the bottom preform surface. These electrodes can join with the conductor ends or can be connected to the conductor ends by known methods. This gives a flexible transducer array that can be used for a variety of applications.

This system uses a cable harness component that is particularly suited for transducer arrays. The cable harness component includes a support structure having a number of predetermined openings made from a viscoelastic material. Flexible circuits with conductors communicate between terminal blocks and electrical contacts within the support structure. Terminal blocks are positioned for outside electrical connection.

This work was done by Kim C. Benjamin of the Naval Undersea Warfare Center. For more information, download the Technical Support Package (free white paper) at www.defensetechbriefs.com/tsp under the Electronics/Computers category. NUWC-0012